Structure-Based Rationalization of the Ionophore Character of Lead-Selective Amide-Ether-Amine-Containing Macrocycles: 2,3-Benzo-1,4-dioxa-7,11,15-triazacycloheptadec-2-ene-6,16-dione and 2,3-Benzo-1,4-dioxa-7,10,13-triazacyclopentadec-2-ene-6,14-dione-Water (1/2)

2,3-Benzo-1,4-dioxa-7,11,15-triazacycloheptadec-2-ene-6,16-dione, C₁₆H₂₃N₃O₄, is a 17-membered ring with an envelope conformation in which amide N and ether O atoms form one plane and the amine N atom lies on the flap. 2,3-Benzo-1,4-dioxa-7,10,13-triazacyclopentadec-2-ene-6,14-dione-water (1/2), C₁₄H₁₉N₃O₄.2H₂O, has a 15-membered ring with all the donor atoms in an approximately planar arrangement. The amide groups of this macrocycle are hydrogen bonded to the water molecules. It appears that the availability of the unsubstituted amine N atom is crucial for the extraction and transport of Pb²⁺ ions. Substitution of a side arm on the amine N atom significantly alters the coordination ability of this N atom in the 17-membered ring and decreases the extraction and transport ability of the macrocycle.

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